Apparatus and method for inspecting a sample using a plurality of charged particle beams

ABSTRACT

An apparatus for inspecting a sample includes a sample holder for holding the sample; a multi beam charged particle generator for generating an array of primary charged particle beams; an electro-magnetic lens system for directing the array of primary charged particle beams into an array of separate focused primary charged particle beams on the sample; a multi-pixel photon detector arranged for detecting photons created by the focused primary charged particle beams when the primary charged particle beams impinge on the sample or after transmission of said primary charged particle beams through the sample; and an optical assembly for conveying photons created by at least two adjacent focused primary charged particle beams of the array of separate focused primary charged particle beams to distinct and/or separate pixels or to distinct and/or separate groups of pixels of the multi-pixel photon detector.

BACKGROUND

The invention relates to an apparatus and a method for inspecting a thinsample. In particular the invention relates to an apparatus forinspecting a sample using a plurality of charged particle beams, such asa multi-beam scanning electron microscope. The invention may be appliedto charged particles of any type, such as electrons, positrons, ions andothers.

Such an apparatus is for example disclosed in A. Mohammadi-Gheidari andP. Kruit “Electron optics of multi-beam scanning electron microscope”Nuclear Instruments and Methods in Physics Research A 645 (2011) 60-67.This publication discloses an electron microscope comprising a electronsource for generating an array of primary charged particle beams, inparticular an array of primary electron beams. These primary electronbeams pass an objective lens which directs the electron beams from acommon cross-over towards the sample and focuses the primary electronbeams into an array of individual spots on the sample. In order to forman image of the sample, it is necessary to detect a characteristicsignal from each beam. In an electron microscope this can be either thesecondary electron signal, or the backscatter electron signal, or thetransmitted electron signal. Methods to detect the secondary electronsignal and the backscatter electron signal have been disclosed inrespectively PCT/NL2013/050416 and PCT/NL2013/050746.

A disadvantage of those methods is that either the detector itself, or abeam separation device needs to be placed in the path of the primaryelectron beams. Another disadvantage of those methods is that theexcitation of the lenses for the primary beams needs to be adjusted inorder to accommodate the signal electron beams. Finally, some contrastmechanisms in the sample to be inspected are better suited fortransmission detection than secondary or backscattered detection.

It is an object of the present invention to provide a multi chargedparticle beam apparatus for inspecting a sample which provides a newdetection arrangement for detecting a signal created by the multiplecharged particle beams.

SUMMARY OF THE INVENTION

According to a first aspect, the invention pertains to an apparatus forinspecting a sample, wherein the apparatus comprises:

a sample holder for holding the sample,

a multi beam charged particle generator for generating an array ofprimary charged particle beams,

an electro-magnetic lens system for directing said array of primarycharged particle beams into an array of separate focused primary chargedparticle beams at the sample holder,

a multi-pixel photon detector arranged for detecting photons created bysaid focused primary charged particle beams when said primary chargedparticle beams impinge on the sample or after transmission of saidprimary charged particle beams through the sample, and

an optical assembly for conveying photons created by at least twoadjacent focused primary charged particle beams of said array ofseparate focused primary charged particle beams to distinct and/orseparate pixels or to distinct and/or separate groups of pixels of themulti-pixel photon detector.

The apparatus of the present invention is arranged to detect photonscreated by said focused primary charged particle beams when said primarycharged particle beams impinge on the sample or after transmission ofsaid primary charged particle beams through the sample, in stead of orin addition to detecting a secondary electron signal and/or abackscatter electron signal. In addition the apparatus of the presentinvention is provided with a multi/pixel detector to detect the createdphotons from two or more focused primary charged particle beams.According to the invention, the optical assembly and/or the multi-pixelphoton detector are arranged to provide a resolution which enables todistinguish a light signal created by one of said at least two adjacentfocused primary charged particle beams from a light signal created bythe other one of said at least two adjacent focused primary chargedparticle beams. The apparatus of the invention thus provides a newdetection arrangement for individually detecting the created photons oftwo or more focused primary charged particle beams simultaneous.

It is noted that the optical assembly can be either arranged at a sideof the sample holder which faces towards the electro-magnetic lenssystem, or at an opposite side of the sample holder which faces awayfrom the electro/magnetic lens system.

A phenomenon which causes the emission of photons due to the impact ofcharged particles on a material, in particular a luminescent material,is referred to as cathodoluminescence. It is noted that in case thesample comprises one or more cathodoluminescent constituents, photonsare created by said focused primary charged particle beams when saidprimary charged particle beams impinge on the sample, in particular thecathodoluminescent constituents thereof.

In an embodiment, said apparatus comprises a layer of cathodoluminescentmaterial, wherein the sample holder is arranged to position the samplebetween the electro-magnetic lens system and the layer ofcathodoluminescent material, such that the charged particles impinge onthe layer of cathodoluminescent material after transmission through saidsample. In this embodiment, the sample does not need to havecathodoluminescent constituents, because the photons are created by saidfocused primary charged particle beams when said primary chargedparticle beams impinge on the layer of cathodoluminescent material aftertransmission of said primary charged particle beams through the sample.

In an embodiment, the layer of cathodoluminescent material is supportedby a light transmitting support plate. On the one hand, the use of asupport plate allows the use of a thin layer of cathodoluminescentmaterial. On the other hand, the use of a light transmitting supportplate allows the created photons to travel through the support plate andallows to arrange the optical assembly and the multi-pixel photondetector at a side of the support plate facing away from the thin layerof cathodoluminescent material.

In an embodiment, said layer of cathodoluminescent material is coveredwith a charge conducting layer, preferably wherein the charge conductinglayer is arranged at a side of said layer of cathodoluminescent materialfacing the electro-magnetic lens system. The charge conducting layerenables to spread and-or remove surface charge induced by the impingingcharged particles. Preferably, in use, the charge conducting layer isconducingly connected to ground potential to lead away the surfacecharge.

In an embodiment, said sample holder is arranged to position the samplein direct contact with and/or supported by said layer ofcathodoluminescent material.

In an alternative embodiment, said sample holder is arranged to positionthe sample at a distance from said layer of cathodoluminescent material.By positioning the sample at a distance from the layer ofcathodoluminescent material, the light signals created by the chargedparticle beams that were not scattered in the sample can bedistinguished from the light signals created by the charged particlesthat were scattered in the sample, in particular for each chargedparticle beam.

In Addition, by arranging the sample at a distance from thecathodoluminescent material, bright field images or dark field imagescan be created. The necessary distance depends on the electron energyand the contrast required. It is also possible to distinguish betweenelectrons scattered in different directions.

In an embodiment, said optical arrangement comprises a lens system whichis arranged for imaging said created photons onto the multi-pixel photondetector with an optical magnification between 5 and 500.

In an embodiment, the electro-magnetic lens system is arranged toproject an array of separate spots on the sample surface where thefocused primary charged particle beams impinge on the sample on thesample holder, wherein the pitch between the spots on the sample surfaceis between 0.3 and 30 micrometers. The beams preferably are sufficientlyseparated that the scattering range of the electrons in the sample orthe cathodoluminescent material is smaller than the distance between theelectron beams. For 5 kV electrons this scattering range is typically300-500 nm. For higher energy electrons this is more. In this situationit is also possible to use a thin layer of cathodoluminescent material,such that the lateral scattering range in the thin layer is smaller thanthe distance between the focused primary charged particle beams.

In an embodiment, the multi-pixel photon detector is a COD camera, aCMOS camera, an array of avalanche photo diodes or an array of photomultipliers.

In an embodiment, the CCD camera, CMOS camera, array of avalanche photodiodes or photo multipliers comprises an array of detector pixels ispositioned such that the array of detector pixels coincides with anarray of images of the individual light spots created by the individualbeams of said primary charged particle beams. In particular the opticalassembly projects or images the individual light spots created by theindividual beams of said primary charged particle beams into the arrayof images.

In an embodiment, said apparatus further comprising a system forscanning the focused primary charge particle beams over said sampleholder. In use, when a sample is arranged on or in said sample holder,the scanning system is arranged for scanning the focused primary chargeparticle beams over said sample. In an embodiment, said apparatusfurther comprises a control-and-signal-processing system for controllingthe scanning system and/or the detector, and/or for creating one imageper primary charged particle beam.

In an embodiment, said apparatus comprising a first actuating system formoving the sample holder at a constant speed in a first direction, and asecond actuating system for scanning the focused primary charge particlebeams over said sample holder in a second direction at leastsubstantially perpendicular to the first direction. In an embodiment,said apparatus further comprises a control-and-signal-processing systemfor controlling the first and second actuating system and/or thedetector, and/or for creating one image per primary charged particlebeam.

In an embodiment, said apparatus further comprises a signal processingunit for combining said individual images per primary charged particlebeam into one combined image of at least a part of the sample.

In an embodiment, said primary charged particle beams comprises electronbeams.

According to a second aspect, the invention pertains to a method forinspecting a sample, using an apparatus comprises:

a sample holder which holds the sample,

a multi beam charged particle generator which generates an array ofprimary charged particle beams,

an electro-magnetic lens system which directs said array of primarycharged particle beams into an array of separate focused primary chargedparticle beams on said sample in or on the sample holder,

a multi-pixel photon detector arranged to detect photons created by saidfocused primary charged particle beams when said primary chargedparticle beams impinge on the sample or after transmission of saidprimary charged particle beams through the sample, and

an optical assembly which conveys the photons created by at least twoadjacent focused primary charged particle beams of said array ofseparate focused primary charged particle beams to distinct and/orseparate pixels or to distinct and/or separate groups of pixels of themulti-pixel photon detector.

In an embodiment of said method, said apparatus comprises a layer ofcathodoluminescent material, wherein the sample holder is arranged toposition the sample between the electro-magnetic lens system and thelayer of cathodoluminescent material, wherein the charged particleswhich pass through said sample, subsequently impinge on the layer ofcathodoluminescent material.

The various aspects and features described and shown in thespecification can be applied, individually, wherever possible. Theseindividual aspects, in particular the aspects and features described inthe attached dependent claims, can be made subject of divisional patentapplications.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be elucidated on the basis of an exemplary embodimentshown in the attached drawings, in which:

FIG. 1 shows an example of a Multi-Beam Scanning Electron Microscope(MBSEM),

FIG. 2 shows a first embodiment of a detection arrangement according tothe invention,

FIG. 3 shows the arrangement of the sample on top of acathodoluminescent layer,

FIG. 4 shows a second embodiment of a detection arrangement according tothe invention,

FIG. 5 shows the arrangement of the sample at a distance from acathodoluminescent layer,

FIG. 6 shows an example of a segmentation of the detection area of adetector,

FIGS. 7A and 7B show an example of a thin cathodoluminescent layer ontop of a light transmitting support plate, and

FIG. 8 shows an example of a cathodoluminescent layer provided with acharge conducting layer.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an example of a Multi-Beam Scanning Electron Microscope(MBSEM) of the invention. The MBSEM 1 comprises a multi beam chargedparticle generator 2 for generating an array of primary charged particlebeams, in this case an array of primary electron beams 3. The multi beamelectron generator 2 comprises at least one electron source 4 forgenerating a diverging electron beam 5. The diverging electron beam 5 issplit into an array of focused primary electron beams 3 by an aperturelens array 6. The primary electron beams 3 are subsequently directedtowards a sample 15 in a sample holder 150, as schematically indicatedby the arrow P.

The multiple images of the source 4 are positioned on the objectprinciple plane of an accelerator lens 7. The accelerator lens 7 directsthe primary electron beams 3 towards the optical axis 8 and creates afirst common cross-over 9 of all the primary electron beams 3.

The first common cross-over 9 is imaged by the magnetic condenser lens10 onto a variable aperture 16 that acts as a current limiting aperture.At the variable aperture 16, a second common cross-over of all theprimary electron beams 3 is created.

The MBSEM comprises a lens system 13, 14 for directing the primarycharged particle beams from the common cross-over at the variableaperture 16 towards the sample surface 15 and for focusing all primarycharged particle beams 3 into an array of individual spots on the samplesurface 15. The lens system comprises an intermediate magnetic lens 13for imaging the variable aperture 16 onto a coma free plane of theobjective lens 14, which objective lens 14 creates an array of focusedprimary electron beams on the sample surface 15.

In addition the MBSEM is provided with scan coils 18 for scanning thearray of focused primary electron beams over the sample surface 15.

The MBSEM thus comprises a multi beam charged particle generator 2 forgenerating an array of primary charged particle beams 3, and anelectro-magnetic lens system 13, 14 for directing said array of primarycharged particle beams 3 into an array of separate focused primarycharged particle beams at said sample 15 in the sample holder 150.

According to the invention, and as schematically shown in a firstexample of FIG. 2, the apparatus further comprises a multi-pixel photondetector 20 arranged for detecting photons 30, 31, 32 created by saidfocused primary charged particle beams 3, 3′, 3″ when said primarycharged particle beams 3, 3′, 3″ impinge on the sample 15. In additionthe apparatus comprises an optical assembly 40 for conveying photons 30,31 created by at least two adjacent focused primary charged particlebeams 3, 3′ of said array of separate focused primary charged particlebeams 3, 3′, 3″ to distinct and/or separate pixels or to distinct and/orseparate groups of pixels of the multi-pixel photon detector 20.

When the sample 15 comprises one or more cathodoluminescentconstituents, photons 30, 31, 32 are created by said focused primarycharged particle beams 3, 3′, 3″ when said primary charged particlebeams 3, 3′, 3″ impinge on the sample 15, in particular on thecathodoluminescent constituents thereof.

However, when the sample 15 does not generate sufficient photons 30, 31,32 to be readily detected by the multi-pixel photon detector 20, a layerof cathodoluminescent material 19 is arranged at a side of the sample 15facing away from the electro-magnetic lens system 13, 14, such that thecharged particles from the primary charged particle beams 3, 3′, 3″impinge on the layer of cathodoluminescent material 19 aftertransmission through said sample 15. In the example as shown in FIG. 3,the sample holder 150 is arranged to position the sample 15 in directcontact with and supported by said layer of cathodoluminescent material19. When the charged particles from the primary charged particle beams3, 3′, 3″ hit the layer of cathodoluminescent material 19, photons arecreated from an interaction volume 190. The size of this interactionvolume 190 and the intensity of the generated light, depends, interalia, on the energy of the charged particles which impinge of the layerof cathodoluminescent material 19.

In a second example of the apparatus of the present invention, asschematically shown in FIG. 4, the sample holder 150 is arranged toposition the sample 15 at a distance d from said layer ofcathodoluminescent material 19. Again, the apparatus comprises amulti-pixel photon detector 20 arranged for detecting photons 30, 31, 32created by charged particle beams 23, 23′, 23″ when they impinge on thelayer of cathodoluminescent material 19 after transmission of theprimary focused charged particle beams 3, 3′, 3″ through sample 15. Theapparatus also comprises an optical assembly 40 for conveying photons30, 31 created by at least two adjacent charged particle beams 23, 23′of said array of transmitted charged particle beams 23, 23′, 23″ todistinct and/or separate pixels or to distinct and/or separate groups ofpixels of the multi-pixel photon detector 20.

The arrangement of the sample 15 and the layer of cathodoluminescentmaterial 19 is shown in more detail in FIG. 5. This figure showsfurthermore that the charged particles of the primary focused chargedparticle beams 3, 3′, 3″ can travel straight through the sample 15.These charged particles are also denoted as 0^(th) order transmittedcharged particles. When the 0^(th) order transmitted charged particleshit the layer of cathodoluminescent material 19, photons are createdfrom an interaction volume 190. When using the photons created by these0^(th) order transmitted charged particles to make an image of thesample, a bright field image is obtained.

In addition, the charged particles of the primary focused chargedparticle beams 3, 3′, 3″ can also be scattered by the sample 15. Thesescattered charged particles exit the sample 15 at an angle with respectto the straight traveling 0^(th) order transmitted charged particles.Because of the distance d between the sample 15 and the layer ofcathodoluminescent material 19, the scattered charged particles end upat a position on the layer of cathodoluminescent material 19 adjacent tothe position of the 0^(th) order transmitted charged particles, asindicated in FIG. 5. When these scattered charged particles hit thelayer of cathodoluminescent material 19, photons are created from aninteraction volume 191. When using the photons created by thesescattered charged particles to make an image of the sample, a dark fieldimage is obtained.

In order to distinguish between a 0^(th) order transmitted chargedparticles and the scattered charged particles, a segmentation of thedetection area of a detector 20 can be used, as for example shown inFIG. 6.

In a first embodiment, the light sensitive area's of the detector 20 isarranged a shown in FIG. 6. Thus for each primary focussed chargedparticle beam there is a group 60, 60′ of light sensitive area's, alsodenoted as pixels, comprising:

a centre light sensitive area 61, 61′ for detecting light generated bythe 0^(th) order transmitted charged particles, and

a ring of light sensitive area's 62, 63, 64, 65, 62′, 63′, 64′, 65′arranged around the centre light sensitive area 61, 61′ for detectinglight generated by the scattered charge particles.

In a second embodiment, the detector 20 comprises a large number ofpixels arranged in rows and columns, which allow to detect any patternof generated light to be detected. From those pattern, the lightgenerated from the individual primary focused charged particles 3, 3′,3″ can be distinguished, because this light is arranged in a group oflight spots. Each of such a group of light spots comprises a centralpart which originated from the interaction volume 190 of the 0^(th)order transmitted charged particles, see for example FIG. 5. Thiscentral part may be surrounded by light spots which originated from theinteraction volume 191 of the scattered charged particles. The signalsfrom these various light spots within the various groups can beseparated using appropriated subroutines for reading out and analysingthe light signals from the pixels of the detector 20.

Alternatively, specific pixels or groups of pixels may be allocated orassigned for example according to the pattern as shown in FIG. 6. Thecentral pixel or group of pixels 61, 61′ is assigned for detecting lightgenerated by the 0^(th) order transmitted charged particles, and thesurrounding pixels or group of pixels 62, 63, 64, 65, 62′, 63′, 64′, 65′are assigned for detecting light generated by the scattered chargeparticles.

In an exemplary embodiment the layer of cathodoluminescent material 19comprises Yttrium aluminium garnet (YAG, Y3Al5O12), which is a syntheticcrystalline material of the garnet group. Although a YAG crystal layerprovides a very homogeneous and well defined layer of cathodoluminescentmaterial, a disadvantageous of a layer of YAG is that it also absorbspart of the generated light. In order to limit the amount of absorptionof the generated light, the layer of cathodoluminescent material 19′ ispreferably a thin layer, preferably smaller or equal to a maximum depthof the interaction volume, which is arranged on top of and/or supportedby a light transmitting support plate 200, as for example shown in FIG.7A.

In an alternative exemplary embodiment, the layer of cathodoluminescentmaterial 19″ is thinner than the maximum depth of the interactionvolume, which is also referred to as the scattering range, as shown inFIG. 7B. The use of such a thin layer of cathodoluminescent material 19″is, that signals from higher energy charged particle beams at leastsubstantially do not interfere.

In addition or alternatively the layer of cathodoluminescent material 19is covered with a charge conducting layer 300, as for example shown inFIG. 8. This charge conducting layer 300 is preferably arranged at aside of said layer of cathodoluminescent material 19 facing theelectro-magnetic lens system 13, 14, and preferably is connected toground potential. The charge conducting layer 300 comprises for examplea layer of ITO and/or graphene. Alternatively or in addition, the chargeconducting layer 300 comprises a thin metal layer, for example having athickness of 10 to 20 nm. Such a thin metal layer provides the desiredcharge conducting properties and in addition provides a mirror effectfor the photons created in the cathodoluminescent material 19, whichmirror effect can increase the part of the created photons which aredirected toward the optical arrangement 40 and the detector 20.

It is noted that the optical arrangement 40 comprises a lens system 41,42 which is arranged for imaging said created photons 30, 31 onto themulti-pixel photon detector 20. Preferably the optical arrangement 40provides an optical magnification between 5 and 500.

In order to obtain an image from the surface of the sample 15, theapparatus further comprising a system 18 for scanning the focusedprimary charge particle beams over said sample, and acontrol-and-signal-processing system 21 for controlling the scanningsystem 18 and the detector 20, and for analyzing the data from thedetector 20 and creating one image per primary charged particle beam.

Alternatively or in addition, the apparatus further comprises a firstactuating system 180 for moving the sample holder 150 at a constantspeed in a first direction. Together with the scanning system 18 as asecond actuating system, for scanning the focused primary chargedparticle beams over said sample in a second direction at leastsubstantially perpendicular to the first direction, the focused primarycharged particle beams can be scanned over an area of the surface of thesample 15. Again the control-and-signal-processing system 21 is forexample arranged to create one image per primary charged particle beam.

The control-and-signal-processing unit 21 is preferably arranged and/orprovided with appropriate subroutines for combining said individualimages per primary charged particle beam into one combined image of atleast a part of the sample 15.

It is to be understood that the above description is included toillustrate the operation of the preferred embodiments and is not meantto limit the scope of the invention. From the above discussion, manyvariations will be apparent to one skilled in the art that would yet beencompassed by the spirit and scope of the present invention.

The invention claimed is:
 1. An apparatus for inspecting a sample,wherein the apparatus comprises: a sample holder for holding the sample,a multi beam charged particle generator for generating an array ofprimary charged particle beams, an electro-magnetic lens system fordirecting said array of primary charged particle beams into an array ofseparate focused primary charged particle beams at said sample holder, amulti-pixel photon detector arranged for detecting photons created bysaid focused primary charged particle beams when said primary chargedparticle beams impinge on the sample or after transmission of saidprimary charged particle beams through the sample, and an opticalassembly for conveying photons created by at least two adjacent focusedprimary charged particle beams of said array of separate focused primarycharged particle beams to distinct and/or separate pixels or to distinctand/or separate groups of pixels of the multi-pixel photon detector,wherein said apparatus comprises a layer of cathodoluminescent material,wherein the sample holder is arranged to position the sample between theelectro-magnetic lens system and the layer of cathodoluminescentmaterial, such that the charged particles impinge on the layer ofcathodoluminescent material after transmission through said sample. 2.The apparatus according to claim 1, wherein the layer ofcathodoluminescent material is supported by a light transmitting supportplate.
 3. The apparatus according to claim 1, wherein said layer ofcathodoluminescent material is covered with a charge conducting layer.4. The apparatus according to claim 3, wherein the charge conductinglayer is arranged at a side of said layer of cathodoluminescent materialfacing the electro-magnetic lens system.
 5. The apparatus according toclaim 1, wherein said sample holder is arranged to position the samplein direct contact with and/or supported by said layer ofcathodoluminescent material.
 6. The apparatus according to claim 1,wherein said sample holder is arranged to position the sample at adistance from said layer of cathodoluminescent material.
 7. Theapparatus according to claim 1, wherein said optical arrangementcomprises a lens system which is arranged for imaging said createdphotons onto the multi-pixel photon detector with an opticalmagnification between 5 and
 500. 8. The apparatus according to claim 1,wherein the electro-magnetic lens system is arranged to project an arrayof separate spots on the sample surface where the focused primarycharged particle beams impinge on the sample on the sample holder,wherein the pitch between the spots on the sample surface is between 0.3and 30 micrometers.
 9. The apparatus according to claim 1, wherein themulti-pixel photon detector is a CCD camera, a CMOS camera, an array ofavalanche photo diodes or an array of photo multipliers.
 10. Theapparatus according to claim 9, wherein the CCD camera, CMOS camera,array of avalanche photo diodes or photo multipliers comprises an arrayof detector pixels is positioned such that the array of detector pixelscoincides with an array of images of the individual light spots createdby the individual beams of said primary charged particle beams.
 11. Theapparatus according to claim 1, further comprising a system for scanningthe focused primary charge particle beams over said sample holder, and acontrol-and-signal-processing system for creating one image per primarycharged particle beam.
 12. The apparatus according to claim 11, whereinsaid apparatus further comprises a signal processing unit for combiningsaid individual images per primary charged particle beam into onecombined image of at least a part of the sample.
 13. The apparatusaccording to claim 1, further comprising a first actuating system formoving the sample holder at a constant speed in a first direction, and asecond actuating system for scanning the focused primary charge particlebeams over said sample holder in a second direction at leastsubstantially perpendicular to the first direction, and acontrol-and-signal-processing system for creating one image per primarycharged particle beam.
 14. The apparatus according to claim 13, whereinsaid apparatus further comprises a signal processing unit for combiningsaid individual images per primary charged particle beam into onecombined image of at least a part of the sample.
 15. A method forinspecting a sample, said method comprising the steps of: providing anapparatus which comprises: a sample holder which holds the sample, amulti beam charged particle generator which generates an array ofprimary charged particle beams, an electro-magnetic lens system whichdirects said array of primary charged particle beams into an array ofseparate focused primary charged particle beams on said sample in or onthe sample holder, a multi-pixel photon detector arranged to detectphotons created by said focused primary charged particle beams when saidprimary charged particle beams impinge on the sample or aftertransmission of said primary charged particle beams through the sample,and an optical assembly which conveys the photons created by at leasttwo adjacent focused primary charged particle beams of said array ofseparate focused primary charged particle beams to distinct and/orseparate pixels or to distinct and/or separate groups of pixels of themulti-pixel photon detector, wherein said apparatus comprises a layer ofcathodoluminescent material, wherein the sample holder is arranged toposition the sample between the electro-magnetic lens system and thelayer of cathodoluminescent material, wherein the charged particleswhich pass through said sample subsequently impinge on the layer ofcathodoluminescent material, the method comprising the steps of:positioning the sample between the electro-magnetic lens system and thelayer of cathodoluminescent material, generating an array of primarycharged particle beams, directing said array of primary charged particlebeams into an array of separate focused primary charged particle beamson said sample, and detecting photons created by said focused primarycharged particle beams when said primary charged particle beams impingeon the sample or after transmission of said primary charged particlebeams through the sample.